--- projects/cms/source/util/uk/org/iscream/cms/util/Queue.java 2001/01/02 03:20:23 1.1 +++ projects/cms/source/util/uk/org/iscream/cms/util/Queue.java 2001/03/22 18:23:27 1.19 @@ -1,10 +1,11 @@ //---PACKAGE DECLARATION--- -package uk.ac.ukc.iscream.util; +package uk.org.iscream.util; //---IMPORTS--- import java.util.LinkedList; import java.util.NoSuchElementException; -import uk.ac.ukc.iscream.util.*; +import java.util.Random; +import uk.org.iscream.util.*; /** * A Queue class designed to operate in a multi-threaded environment, with @@ -13,20 +14,73 @@ import uk.ac.ukc.iscream.util.*; * actually contains some elements. * * @author $Author: tdb $ - * @version $Id: Queue.java,v 1.1 2001/01/02 03:20:23 tdb Exp $ + * @version $Id: Queue.java,v 1.19 2001/03/22 18:23:27 tdb Exp $ */ -class Queue { +public class Queue { //---FINAL ATTRIBUTES--- /** * The current CVS revision of this class */ - public static final String REVISION = "$Revision: 1.1 $"; + public static final String REVISION = "$Revision: 1.19 $"; + /** + * Pass to constructor to remove a RANDOM item from + * the Queue upon reaching the maximum limit. + */ + public static final int RANDOM = 0; + + /** + * Pass to constructor to remove the FIRST item from + * the Queue upon reaching the maximum limit. + */ + public static final int FIRST = 1; + + /** + * Pass to constructor to remove the LAST item from + * the Queue upon reaching the maximum limit. + */ + public static final int LAST = 2; + + /** + * Pass to constructor to drop the new item upon reaching + * the maximum Queue limit. + */ + public static final int DROP = 3; + + /** + * To allow opposite lookups. + */ + public static final String[] algorithms = {"RANDOM", "FIRST", "LAST", "DROP"}; + //---STATIC METHODS--- //---CONSTRUCTORS--- + + /** + * Constructs a new Queue with a maximum size limit on + * any individual queue. This should be used to stop + * conditions where the Queue cannot be guaranteed to + * be emptied as quick as it's filled. + * + * An algorithm will be used to remove data when new data + * arrives. There may be choices of algorithms later on. + * + * @param maxSize the upper limit for a queue + * @param removeAlgorithm the remove algorithm to use upon reaching the maxSize + */ + public Queue(int maxSize, int removeAlgorithm) { + _maxSize = maxSize; + _removeAlgorithm = removeAlgorithm; + } + + /** + * Constructs a Queue with no maximum size. + */ + public Queue() { + _maxSize = -1; + } //---PUBLIC METHODS--- @@ -40,11 +94,21 @@ class Queue { for(int i=0; i < _lists.size(); i++) { // skip over any gaps left in the list if(_lists.get(i) != null) { + // get size before adding to the Queue int s = ((LinkedList) _lists.get(i)).size(); - synchronized(this) { - // add() does the same thing, but this ensures behaviour - ((LinkedList) _lists.get(i)).addLast(o); + // check whether we need to remove an item from the current Queue + if(_maxSize!=-1 && s==_maxSize && _removeAlgorithm!=DROP) { + // we need to remove an item + removeQueueItem((LinkedList) _lists.get(i)); } + // check if we should add (not if Queue full, and using DROP algorithm) + if(!(s==_maxSize && _removeAlgorithm==DROP)) { + // add the next item, ensuring we lock + synchronized(this) { + // LinkedList.add() does the same thing, but this ensures behaviour + ((LinkedList) _lists.get(i)).addLast(o); + } + } // if the queue was empty before the add it is possible // that a consumer is waiting... so we notify them if (s == 0) { @@ -62,6 +126,7 @@ class Queue { * This method returns an object from the front of a given queue. * It will block until data exists in the queue if required. * + * @param The queue to retrieve data from. * @return The object from the front of the queue. * @throws InvalidQueueException if the queue does not exist. */ @@ -71,8 +136,8 @@ class Queue { throw new InvalidQueueException("Requested queue "+queue+" does not exist"); } // block if the queue is empty - if (((LinkedList) _lists.get(queue)).size() == 0) { - synchronized(((LinkedList) _lists.get(queue))) { + synchronized(((LinkedList) _lists.get(queue))) { + if (((LinkedList) _lists.get(queue)).size() == 0) { try { ((LinkedList) _lists.get(queue)).wait(); } catch(Exception e) {} } } @@ -88,34 +153,90 @@ class Queue { } return o; } - + /** - * This method returns a textual status of the queues. It - * is merely for observation, and would most likely be used - * by a larger "monitoring" component. Information returned - * includes the current size of each queue, and the total - * items passed through. + * This method releases a get() method that's currently + * waiting on an empty queue. This was designed for + * shutdown() type methods that may have problems closing + * if the thread of control is waiting on a queue. * - * @return A String message containing status information. + * @param queue the queue to release. */ - public String status() { - String status = ""; + public void releaseQueue(int queue) { + synchronized(((LinkedList) _lists.get(queue))) { + ((LinkedList) _lists.get(queue)).notifyAll(); + } + } + + /** + * This method erases the contents of a given queue. This + * method should be used with care. It can only empty one + * internal queue, not all of them. This must be called + * multiple times to empty all queues. + * + * @param queue the queue to empty. + */ + public void clearQueue(int queue) { + synchronized(this) { + ((LinkedList) _lists.get(queue)).clear(); + } + } + + /** + * This method returns an XML textual status of the queues. + * It is merely for observation, and would most likely be + * used by a larger "monitoring" component. Information + * returned includes the current size of each queue, and + * the total items passed through. + * + * @return A String message containing status information in XML format + */ + public String xmlStatus() { + String status = "= _lists.size() || _lists.get(queue) == null) { + throw new InvalidQueueException("Requested queue "+queue+" does not exist"); + } + return ((LinkedList) _lists.get(queue)).size(); + } + + /** + * Returns the total numer of elements to have passed + * through this queue (ie. a counter on the add method). + * + * @return the element-ometer. + */ + public int elementCount() { + return _count; + } + + /** * This method assigns a queue to a consumer. The idea behind * this is to ensure that only 1 consumer can be associated with * a given queue, otherwise the whole "blocking" thing fails @@ -126,7 +247,7 @@ class Queue { * * @return An integer to be passed to the get() method. */ - public int getQueue() { + public synchronized int getQueue() { int pos = -1; for(int i=0; i < _lists.size(); i++) { if(_lists.get(i) == null) { @@ -150,28 +271,112 @@ class Queue { * * @param queue The integer identifier for the queue, given by getQueue(). */ - public void removeQueue(int queue) { + public synchronized void removeQueue(int queue) { _lists.set(queue, null); } /** + * Start a monitor on our own Queue. This will log XML + * statistics about our Queue to a given Queue (could be + * the one being monitored). + * + * @param interval The long interval, in milliseconds, at which to take samples + * @param destQueue The queue to monitor to + * @param name A name to identify this Queue with + * @return whether we succeeded + */ + public boolean startMonitor(long interval, Queue destQueue, String name) { + if(_queueMon == null) { + // start a monitor + _queueMon = new QueueMonitor(this, destQueue, interval, name); + _queueMon.start(); + return true; + } + else { + // already have a monitor running + return false; + } + } + + /** + * Start a monitor on our own Queue. This will log XML + * statistics about our Queue to this Queue. + * + * @param interval The long interval, in milliseconds, at which to take samples + * @param name A name to identify this Queue with + * @return whether we succeeded + */ + public boolean startMonitor(long interval, String name) { + return startMonitor(interval, this, name); + } + + /** + * Stop a monitor on our Queue if we have on running. + * + * @return whether we succeeded + */ + public boolean stopMonitor() { + if(_queueMon != null) { + // stop a monitor + _queueMon.shutdown(); + _queueMon = null; + return true; + } + else { + // no monitor running + return false; + } + } + + /** * Overrides the {@link java.lang.Object#toString() Object.toString()} * method to provide clean logging (every class should have this). * - * This uses the uk.ac.ukc.iscream.util.FormatName class + * This uses the uk.org.iscream.util.FormatName class * to format the toString() * - * @return the name of this class and its CVS revision + * @return the name of this class and its CVS revision. */ - /*public String toString() { + public String toString() { return FormatName.getName( _name, getClass().getName(), REVISION); - }*/ + } //---PRIVATE METHODS--- - + + /** + * This method removes an item from a Queue, using a method + * requested at construction. + * + * @param list The LinkedList from which to remove an item. + */ + private void removeQueueItem(LinkedList list) { + // look at our algorithm + // remove a random item from the list + if(_removeAlgorithm==RANDOM) { + // new Random, with a good seed + Random rand = new Random(System.currentTimeMillis()); + int i = rand.nextInt(_maxSize); + synchronized(this) { + list.remove(i); + } + } + // remove the first item from the list + else if(_removeAlgorithm==FIRST) { + synchronized(this) { + list.removeFirst(); + } + } + // remove the last item from the list + else if(_removeAlgorithm==LAST) { + synchronized(this) { + list.removeLast(); + } + } + } + //---ACCESSOR/MUTATOR METHODS--- //---ATTRIBUTES--- @@ -188,6 +393,22 @@ class Queue { private int _count = 0; /** + * A reference to our QueueMonitor, if we have one. + */ + private QueueMonitor _queueMon = null; + + /** + * The maximum size of any Queue. + */ + private int _maxSize = -1; + + /** + * The remove algorithm to use upon a Queue reaching + * it's maximum size. + */ + private int _removeAlgorithm = -1; + + /** * This is the friendly identifier of the * component this class is running in. * eg, a Filter may be called "filter1", @@ -196,13 +417,7 @@ class Queue { * can be placed here. This name could also * be changed to null for utility classes. */ - //private String _name = ; - - /** - * This holds a reference to the - * system logger that is being used. - */ - //private Logger _logger = ReferenceManager.getInstance().getLogger(); + private String _name = null; //---STATIC ATTRIBUTES---